The field of art to which this invention pertains is homopolymers of 4-hydroxystyrene.
Homopolymers and copolymers of 4-hydroxystyrene, or p-vinylphenol as it is also called, are known compositions which have been used, for example, in the manufacture of metal treatment compositions, photoresists, epoxy resins and epoxy resin curing agents. Polymers of 4-hydroxystyrene can be made by polymerizing 4-hydroxystyrene itself. However, 4-hydroxystyrene is an unstable compound and must be refrigerated to prevent it from polymerizing spontaneously. Even under refrigeration, the monomer will slowly polymerize to low molecular weight polymers. 4-Acetoxystyrene, the acetic acid ester of 4-hydroxystyrene, is a stable monomer which can be readily homopolymerized and copolymerized to low, medium and high molecular weight polymers. After polymerization, the phenolic ester group can be hydrolyzed to produce 4-hydroxystyrene polymers.
Corson et. al., Journal of Organic Chemistry, 23, 544-549 (1958), describe a 5 step process for making 4-hydroxystyrene from phenol. The phenol is first acetylated to 4-hydroxyacetophenone which is then acetylated to 4-acetoxyacetophenone. This compound is hydrogenated to 4-acetoxyphenylmethyl carbinol which is then dehydrated to 4-acetoxystyrene. The 4-acetoxystyrene is saponified to 4-hydroxystyrene using potassium hydroxide.
The ester interchange reaction of poly(4-acetoxystyrene) in methanol using sodium methylate is described in U.S. Pat. No. 2,276,138. About 84 percent of the acetate groups are removed by the interchange reaction. Packham, in the Journal of the Chemical Society, 1964, 2617-2624, describes the hydrolysis of crosslinked poly(4-hydroxystyrene) by refluxing the polymer in alkaline aqueous dioxane for 2 days. In U.S. Pat. No. 4,544,704, a copolymer of styrene and p-isopropenylphenylacetate is hydrolyzed with aqueous sodium hydroxide in methanol and toluene using a small amount of benzyltrimethylammonium chloride as a phase transfer agent. Arshady et. al., Journal of Polymer Science, 12, 2017-2025 (1974), hydrolyzed copolymers of styrene and acetoxystyrene to the vinylphenol polymer using hydrazine hydrate in dioxane.
In copending commonly assigned patent application Ser. No. 007,541, filed Jan. 28, 1987, now abandoned aqueous emulsions of polymers of 4-acetoxystyrene are hydrolyzed with a base to polymers of 4-hydroxystyrene.
In these prior art processes, the vinylphenol polymer is usually recovered as a solution. In order to obtain the polymer in solid form, it must be recovered from the solution by some means, such as by precipitation with a nonsolvent, acidification of the salt form of the polymer, spray drying, or the like. Such processes are time consuming and expensive, requiring additives and/or energy.